Similar to the related applications discussed above, the invention disclosed here is designed to be used in conjunction with a rotary wire stripper of a type disclosed in U.S. Pat. No. 4,745,828, issued to Stepan on May 24, 1988. With this type of stripper, the distance of inward blade movement is operator selectable so that a single machine is capable of stripping a wide range of wire types and sizes. Hereafter, such stripper will be referred to simply as the '828 stripper. Although it is to be understood that the description of the invention set forth here is specifically directed to improving the operation of such stripper, the invention is also wellsuited for use in conjunction with other kinds of strippers as well.
A review of the above co-pending applications reveals that both are concerned with the problem of stripping the insulation from the end of a wire without the blade nicking or scraping the wire's center conductor. In particular, the applications are directed to aerospace applications where such nicking or scraping is undesirable, and generally is not allowed. The applications called the piece of insulation removed from the wire's end a "slug," and the same terminology will sometimes be employed here
The '178 application relates to an improved wire guide for the '828 stripper which better serves to hold both the slug and the wire's center conductor in a fixed position relative to the stripper's blades, and prevents the center conductor from jiggling back and forth into contact with the blades after the slug has been cut all the way through, and while it is pulled or stripped from the wire's end.
The '181 application discloses an improved blade that enables cutting or chipping through insulation without causing much pressure build-up by the blades as they cut, and is particularly directed to hard, glass-like forms of insulation. As was explained there, using conventional blades to cut through hard insulation creates a high pressure build-up between the blades' cutting edges and the insulation. The sudden release of pressure that occurs when the blades break through the insulation causes them to overtravel and contact and nick the center conductor.
The present invention deals with still another aspect of improving the '828 stripper that is unrelated to the specific solutions to center conductor nicking and scraping provided by the '828 and '178 applications, although the invention is concerned with the same overall problem. Unlike the '828 and '178 applications, however, the present invention is solely directed to the various aspects of controlling blade closure of the stripper, and improves such control in order to avoid nicking and scraping.
Referring to FIG. 2 herein, for example, which is labeled "Prior Art," generally shown at 1 is a commercial embodiment of the '828 stripper. Such embodiment is known in the trade as a Schlueniger Model 207S wire stripper, and when such model designation is called out here, it is to be understood that it and the '828 stripper are generally one and the same.
A review of the '828 patent reveals that such stripper 1 includes many components, and it is to be understood by the reader that the disclosure of such patent is incorporated herein by reference. Although it is not necessary, in order to understand the present invention, that each and every component of the stripper 1 shown in FIG. 1 be explained, what follows will be a general description of certain stripper components. Such description should be sufficient to make it clear to the reader what the differences are between the '828 stripper, as originally disclosed in its underlying patent, and the improvements for such stripper which are the thrust of the present invention.
Briefly, the stripper 1 has a casing or housing structure 3 that both receives and provides mounting structure for the various other stripper components. The stripper 1 has two diametrically-opposed blades 5, 7, which are driven in rotation around the end of a wire that is to be stripped (the wire is not shown in FIG. 1). Simultaneously, the blades 5, 7 move generally radially inwardly, coming into contact with the wire's insulation, and cutting through its thickness.
FIG. 4 illustrates the stripper's blade-drive assembly, which is indicated generally at 9. This assembly includes a hollow, electrically conductive drive shaft 11, and a head assembly 13 mounted to one end of the shaft, the latter carrying blades 5, 7. The head assembly 13 also carries wire guides 5A, 7A that are positioned adjacent the blades 5, 7. These will not be further described here as they are not germane to the present invention. Any questions concerning such guides can be answered by referring to the '828 patent, or to the '178 application which is soon to be published as a U.S. patent.
Rotation of shaft 11 in turn rotates blades 5, 7 around the wire that is to be stripped (not shown in FIG. 4, but see FIG. 8, for example). As is explained in detail in the '828 patent, the head assembly 13 has a pair of lever arms 15, 17 which are rotatably mounted to head assembly 13, and an actuation bevel 19. Shaft 11 contains an axially-extending thrust tube 21 that moves actuation bevel 19 linearly for symmetrically pivoting lever arms 15, 17 as shaft 11 rotates. When actuation bevel 19 moves from right to left, for example, this causes the stripper blades 5, 7 to simultaneously move radially inwardly in circling fashion toward the wire to be stripped, until their edges contact and cut through the wire's insulation. Thrust tube 21 is also hollow, the reason for which is clear in the '828 patent. FIG. 15 shows the blade-drive assembly 9 mounted to the stripper's housing structure 3, where the top of the housing has been removed in order to provide a better view of the housing's interior. The stripper 1 has motors that control the rate of blade closure of the blade-drive assembly 9, shown in FIG. 4, and also the linear reciprocation of such assembly back and forth for stripping the end of a wire. The latter motion is adequately described in the '828 patent, and need not be repeated in great detail here. Referring to FIG. 16, what is generally pertinent to the present invention, however, is that the stripper 1 has two motors, one a conventional motor 23 and the other a conventional servodrive 25 (see also FIGS. 3 and 5), whose function is to respectively rotate the stripper's blades 5, 7 and move them inwardly or outwardly.
As is clearly shown in FIG. 16, motor 23 rotates shaft 11 by means of a conventional belt and pulley arrangement that is indicated generally at 27. Blade closure is simultaneously accomplished by servodrive 25 that is mounted to a traveling bracket 29. Such bracket 29 moves back and forth with the blade-drive assembly 9, and it is driven by another servodrive 31 that is in engagement with bracket 29 via a worm gear.
Servodrive 25 controls blade closure. That is to say, servodrive 25 drives another sliding bracket 37 via worm gear 35. The latter bracket 37 is fixedly connected to the end of thrust tube 21 which, as described above, drivingly moves actuation bevel 19.
Typically, the period of rotation of blades 5, 7 is set by electronic controls, and the motor 23, which actually drives rotation or the circling movement of the blades' is controlled by a voltage pulse of fixed duration This is shown at 39 in FIG. 5. The inward movement of the blades 5, 7 is also controlled by a voltage pulse 41 of fixed duration, but one that is voltage-variable in amplitude depending on the selected end-point of inward blade movement.
For example, a certain fixed voltage (Vopen) applied to the control of servodrive 25 signifies a totally "open" blade position, as indicated at 43 in FIG. 5. A certain end-point voltage (Vout) is defined when the operator selects the depth of the cut into the wire's insulation, or the final gap between the stripper's blades 5, 7 at their inwardmost position. This is indicated at 45 in FIG. 5, which also shows that the cycle times for both blade rotation and blade closure are substantially identical in the '828 stripper. The control circuitry of the '828 stripper linearly decreases the magnitude of the servodrive's control voltage from Vopen to Vout as shown at 41.
The arrangement illustrated at 41, 43, 45 in FIG. 5 forces the blade's cut depth to be fixed in accordance with values selected by the operator, based upon typical dimensions of the wire being stripped, without regard to actual variable conditions that may be present during wire stripping. By way of illustration, the operator of the stripper 1 selects or defines the end-point voltage 45 based on the diameter of a given wire that is about to be stripped. Such diameter is given to the operator by the wire's manufacturer, and will have a certain standard or conventional value such as, for example, 0.025 inches. The operator accordingly selects an end-point voltage that corresponds to setting a 0.025 gap between the cutting edges of blades 5, 7 at the end of their inward travel. Of course, what actually happens, by way of clarification, is that the operator sets the gap on the '828 stripper and that defines the magnitude of the end-point voltage.
Such setting is selected assuming that the conductor is concentric relative to the wire's insulation, and that the stripper's wire guides hold the wire exactly at the mid-point between the blades 5, 7. In actuality, such assumptions are generally not true. It is typical, for example, that the true diameter of the wire's center conductor may vary somewhat from manufacturer specifications, or from the 0.025 inches in the illustration given above, and the conductor is rarely exactly concentric relative to the surrounding insulation. This means that the selected gap often does not match the center conductor's true diameter, and the center conductor is typically off-set from the mid-point between the blades 5, 7. Therefore, selecting a nonvariable end-point voltage 45 fixes the inward travel of blade movement, regardless of these kinds of variations, and causes nicking or scraping of the wire's center conductor if the wire is out-of-round, or if its true diameter is different from the one specified by the operator.
To reiterate what was said in the co-pending applications identified above, nicking is impermissible in certain kinds of manufacturing environments, and particularly, in aircraft manufacturing. As a person skilled in the art would know, it is typical that a wire's center conductor consists of a plurality of small strands of copper that are twisted or braided together, instead of a single copper wire. Such strands are typically plated with a protective coating. Nicking one or more strands removes such coating, thus creating a potential for the on-set of long-term corrosion.
One drawback associated with the stripper disclosed in the '828 patent is that it has no means for detecting and controlling blade proximity relative to the wire's center conductor, and to accommodate for variations or deviations in the conductor's expected diameter or location. This has made it difficult or impossible to universally implement a single '828 stripper for stripping all kinds of wires, at least in the aircraft manufacturing industry where center conductor nicking is not allowed.
A second drawback associated with the '828 stripper is that it too quickly closes the blades 5, 7 on the wire to be stripped. This creates poor cutting or stripping quality in that it tends to fray the wire's insulation rather than cut it cleanly, and it also exacerbates center conductor nicking because it creates a higher level of blade dynamic motion. The latter causes the blades 5, 7 to physically travel beyond the point set by Vcut 45.
Up to the present, aircraft manufacturers have not been able to use the '828 stripper because of the nicking problems associated therewith. Instead, such manufacturers have used a multitude of fixed blade strippers, each of which is unique for a particular wire type or size that is to be used on an airplane. As will become apparent, implementation of the present invention improves the performance of the '828 stripper, and similar kinds of strippers, in that it makes them functional for use in manufacturing environments where nicking cannot be tolerated. The way the invention accomplishes this will become understood after consideration of the following.